diff --git a/mixer/v1/global_dictionary.yaml b/mixer/v1/global_dictionary.yaml
index 7627f9777f..01f9e569df 100644
--- a/mixer/v1/global_dictionary.yaml
+++ b/mixer/v1/global_dictionary.yaml
@@ -295,3 +295,25 @@
 # query_params is the normalized query part of a url.
 - request.url_path
 - request.query_params
+
+# context.proxy_error_code = %RESPONSE_FLAGS% in envoy access logs.
+# Other proxies should return equivalent error messages.
+- context.proxy_error_code
+# following are the RESPONSE_FLAGS supported by envoy as of 2018-08-10
+# https://www.envoyproxy.io/docs/envoy/latest/configuration/access_log#configuration
+- UH
+- UF
+- UO
+- NR
+- LH
+- UT
+- LR
+- UR
+- UC
+- DI
+- FI
+- RL
+- "-"
+
+- inbound
+- outbound